Phase of clinical testing uses the fewest number of subjects and establishes the dose at which signs of toxicity appear?

The phase of clinical testing that uses the fewest number of subjects and establishes the dose at which signs of toxicity appear is Phase 1. In this phase, the primary focus is on assessing the safety, tolerability, and pharmacokinetics of a drug in a small group of healthy volunteers or patients. It typically involves a limited number of participants, often ranging from 20 to 100, to determine the maximum tolerated dose and identify any adverse effects.